1. Field of the Invention
The present invention relates to a structure of a gas engine for reducing the ratio of misfire generated at the time of activating a pilot oil ignition type gas engine, and increasing the activation stability, and also relates to an operating method of the gas engine.
2. Description of Related Art
Since pilot ignition type gas engines, which perform compression ignition, have higher ignition energy than conventional spark plug ignition type gas engines, they can achieve a far greater increase in output. However, a pilot ignition oil type gas engine is also ignited by a spark plug or the like, since compression ignition is difficult at the time of activating in a low-temperature combustion chamber. Therefore, to make the engine more economical by reducing the number of its components, or to achieve smoother activation, there is a need to adjust conditions so as to enable earlier compression ignition and realize pilot oil ignition operation from the cranking time.
FIG. 1 is a cross-sectional view of the region near a cylinder head 1 of a pilot oil ignition type gas engine proposed by the present inventors. A spark plug 4 for activation is provided in a main combustion chamber 2 in which a piston 3 rises and falls. Furthermore, a preparatory combustion chamber 5 for pilot oil ignition leads to the main combustion chamber 2. A pilot oil fuel valve 6 is provided inside the preparatory combustion chamber 5. The pilot oil fuel valve 6 is connected via a pipe 8 to a pilot oil pump 7. The pilot oil pump 7 is driven by the driving force of the gas engine. Although not illustrated in FIG. 1, the pilot oil pump 7 is connected via a pipe to a pilot oil tank. Furthermore, although not illustrated in FIG. 1, gas fuel is supplied from a fuel supply source via a fuel supply valve to the main combustion chamber 2.
At the time of activation, a spark is generated by the electrode of the spark plug 4 at an appropriate timing, and the gas fuel supplied into the main combustion chamber 2 is ignited. The pilot oil is forced to the pilot oil fuel valve 6 by the pilot oil pump 7 which is driven by the engine. The pressure applied to the pilot oil increases as the number of rotations of the engine increases, and the pilot oil starts to spray into the preparatory combustion chamber 5 at the point where this pressure exceeds the valve-open pressure of the pilot oil fuel valve 6. Then, when the temperature inside the preparatory combustion chamber 5 at the time of spraying the pilot oil has exceeded the self-ignition temperature of the pilot oil, the pilot oil ignition operation begins, and the spark plug 4 stops sparking.
When misfire is generated during the activation, uncombusted gas is released into the exhaust. When the ratio of generated misfire increases, so does the density of combustion gas in the exhaust pipe, and, when the gas density reaches a flammable range, there is a danger of sudden combustion in the exhaust pipe. Furthermore, when the ratio of misfire increases, the engine may fail to activate (stall).
Therefore, in a system using a gas engine, it is important to reduce misfire at the time of activation.